The present invention relates, in general, to a method and apparatus for producing a workpiece and, more specifically, to a method and apparatus that tracks and maintains a part processing record during the production of the workpiece.
An example that will be used in describing the present invention is that of an automotive industry production line. However, it should be noted that the present invention is not limited to such production lines.
In general, production lines, or systems, are a combination of machines, or processes. A machine is composed of one or more stations with each station having one or more mechanisms. These mechanisms can additionally be broken down into their constituent elements.
Errors in processing and damage to workpieces and stations occur from a failure of the individual stations to be informed of the part processing record of the workpiece. As an example, the manufacture of automotive engine blocks will be used. If a hole is drilled in the block at one station and then the hole is tapped at another station, a great deal of damage can be done to the tapping station if the hole was not drilled, or drilled improperly, at the drilling station. Additionally, the block may be damaged in such an instance rendering it unrepairable.
In an effort to avoid these types of problems, individual stations have been equipped with probes, such as a full depth probe in this example, that will check the block before the tapping station to see if the workpiece is in condition to be tapped. While this inspection saves damage to the stations, and possibly the blocks, it has increased the operating time of the station to perform this check. This additional time in processing can increase the cost of a completed product significantly. Further, these probes increase the cost of the station and insert another mechanism that may malfunction.
Another problem that exists is that of having the same station performing multiple cycles on the same workpiece. This error can occur when several stations do not operate with equal cycle times. For instance, it may take the drilling station three times the amount of time to drill a hole as it does the tapping station to tap a hole. When the order comes in to execute, or cycle, the tapping station will tap the hole, pull back and still see the command to cycle. Seeing this command, the tapping station will again attempt to tap the hole. Logical latches are used to avoid this problem by allowing each station to cycle only once. The transfer of parts then acts to release the logical latch.
In addition, it is difficult, if at all possible, in prior art production lines to insert a partially completed workpiece at the beginning of a line and have only the functions performed on the workpiece that are required. Further, it may be desirable to insert a partially finished workpiece in the middle of a production line. This insertion would also be difficult as the system would have no way of knowing what operations had and had not been performed.
One patent in the area of manufacturing is U.S. Pat. No. 4,509,123 issued to Vereen. This patent describes an automated tracking process for manufacturing and inventory. More specifically, the patent describes a process for manufacturing garments by placing a tag, or similar item, having a machine readable code on the bundles. These tags are scanned at each work place to register the operator, machine, and time the bundle was completed at that station. However, there is no communication from the system storing the information back to the stations. As a result, there is no way to inform a downstream operator that an upstream operator, or station, has or has not performed its work on the bundle. In other words, there is no way to inhibit the present operator from working on the bundle based on some previous operators action.
Another patent is U.S. Pat. No. 3,765,763 issued to Nygaard. This patent describes an automatic slice (semiconductor wafer) processor. In this patent, a machine readable code is etched on a portion of the wafer. At various points in the production line, the codes are read to insure that the wafers stay in order during processing. However, there is no method to stop (inhibit) the downstream processing of a wafer if an upstream operation was not performed correctly. Further, it is not possible to start a wafer in mid-stream on the production line.
Accordingly, it is an object of the present invention to provide a method and apparatus of processing a workpiece that overcomes the above deficiencies.
A further object of the present invention is to provide a method and apparatus of monitoring a part processing record during the production of the workpiece.
Another object of the present invention is to provide a method and apparatus of processing a workpiece in which operation at a work station can be inhibited by a part processing record of the workpiece.
Still another object of the present invention is to provide a method and apparatus of processing a workpiece in which a current part processing record of all workpieces currently in process is maintained at each work station.
Yet another object of the present invention is to provide a method and apparatus of processing a workpiece which is more economical to utilize.